High-mobility channel materials, such as III-V materials, have been proposed as alternatives to replace Silicon as the channel material for complementary metal-oxide-semiconductor (CMOS) applications, due to their intrinsic high electron mobility. Semiconductor substrates comprised of an extremely thin III-V material on an insulator, for example, have been identified as a promising substrate for making field-effect transistors (FETs) with improved scaling, while also offering improved electrostatic behavior over bulk counterparts.
The proper surface passivation of III-V materials, however, has been recognized as an overriding challenge in realizing high-performance inversion-type III-V FETs. The high density of charge traps at the interface between the insulator layer and the III-V material can result in significant degradation of carrier transport in the channel. In addition, the reduction of carrier density in the channel due to charge trapping can also result in significant degradation of drive current.
S. H. Kim et al., “High Performance Extremely-Thin Body III-V-on-Insulator MOSFETs on a Si Substrate with Ni—InGaAs Metal S/D and MOS Interface Buffer Engineering,” IEEE Symp. on VLSI Technology (VLSIT) (2011), proposes the insertion of a buffer layer comprised of Indium Gallium Arsenide (InGaAs) in between the channel and the insulator. The disclosed technique employs an InGaAs buffer layer with a lower Indium content than that of the InGaAs channel to confine electron carriers in the channel. The employed buffer layer, however, does not have a sufficiently large conduction band offset with the conduction band of the channel material to repel electrons.
A need therefore remains for improved semiconductor substrates employing a wide bandgap material between the channel and the insulator. Yet another need exists for the employed wide bandgap material to provide a sufficiently large conduction band offset with the conduction band of the channel material to repel electrons. Although III-V channel materials offer high electron mobility, their relatively low effective conduction band density of states will have a negative impact on the inversion charge density and the resulting drive current. Therefore, a device structure is also needed that can circumvent this low effective conduction band density problem as well.